In, for example, the scanning of photographic film or the like by laser beams to deposit pixels on the film, there is sometimes a very serious need for exceptional registration. This registration refers to the ability to establish on the photographic film pixel positions which are repeated with respect to a sequence of sheets which may subsequently be used cooperatively to form a composite image. Thus, for example, in the formation of a composite image with a plurality of colors these colors must be accurately placed on respective of a sequence of sheets in order that they can become properly combined to produce cooperatively a composite arrangement of colors. Such colors may also have to be aligned with a black and white arrangement which constitutes a text thus providing a further need for exceptional registration. Registration has to be effected between the pixel positions themselves which in turn may be registered relative to targets positioned on the respective sheets. These targets may take the form of cross lines arranged in the form of a plus sign or an X.
The achieving of registration has always been elusive and erratic in roll fed images. This has been due to the fact that using rollers to grab film requires high pressures and usually a large wrap around relative to the drive roller thus causing dimensional deformation of the photographic media or film (actually the medium can be film, photographic paper, or paper or plastic plate material). The reason that good registration is desired for roll fed images is that roll fed devices are inherently much faster than the other devices now used to obtain good registration. These other devices include sheet fed devices using drums or flat beds with various clamping means such as vacuums or pins, or quasi-sheet fed devices wherein sheets are pre-cut from a roll and then clamped by various means such as mentioned above.
Another reason for the desire to obtain good registration with roll (or web) fed devices is that good registration is required for the production of color separations in color printing. The use of known drum or flat bed devices to produce color separations is slow, therefore encouraging the use of roll fed images to produce black and white images and types on pages. This requires that the color picture and the type be then merged by cutting and pasting (a process known as stripping), and then photographing the merged page to create the separation plates for printing. This is labor intensive, consumes time, and consumes material (i.e., film) all of which is costly.
By using a roll fed imager capable of good registration, it is possible not only to produce type and color separations with the same imager, but also to produce them merged on the same page, thereby totally eliminating the stripping process. In addition, since roll fed devices are fast (that is why they are usually used to produce black and white and type), this registration capability makes it possible to produce color as well as black and white very quickly. This is particularly important in high production environments such as newspapers (which are steadily progressing to the use of color pages).
Photographic film and paper used for phototypesetting and other image recording applications as discussed herein include various typical commercial brands such as Kodak "Pagi Set" or Kodak Helium Neon Laser Film 2692, DuPont "Cronatype", or DuPont Helium-Neon CRT Film(CHC-4), Paper(CHE-P), Chemco "Powermatic", and Amitec "Reprotype".